Aiming at the typical faults of current sensors in permanent magnet synchronous motor (PMSM) drive system, a fault diagnosis method of current sensors based on the second-order difference is proposed. The fault sensor is located by judging the relationship between the current residual and the threshold, and the fault type is identified by calculating the second-order difference and periodic current integral of the output current. The proposed method can accurately identify four typical current sensor faults, providing accurate information for fault tolerance and maintenance. Meanwhile, the robustness of the algorithm is enhanced due to the periodic reconstruction of current residual. Simulation and experimental results show that the proposed method can locate and identify fault sensors accurately, and it is robust to parameter mismatches and current disturbances.